Addition of hydrogen and C2 to C4 hydrocarbons to the feed gas in the catalytic conversion of methane to higher molecular weight hydrocarbons

ABSTRACT

Disclosed is a continuous catalytic process for the production of higher molecular weight hydrocarbons from methane in which a methane-containing gas is contacted in a reaction zone with a higher molecular weight hydrocarbon synthesis catalyst under C 2  +hydrocarbon synthesis conditions, the improvement comprising adding a C 2  to C 4  hydrocarbon and hydrogen to said gas thereby forming a reaction gas wherein said C 2  to C 4  hydrocarbon comprises 0.1 to 10 volume percent of said reaction gas and said hydrogen comprises 1 to 25 volume percent of said reaction gas, said synthesis conditions including a temperature greater than 1000° C. and a gas hourly space velocity of greater than 3200 hr 31  1.

FIELD OF THE INVENTION

The present invention relates to a catalytic process for the productionof higher molecular weight hydrocarbons from methane. More particularly,the present invention relates to the conversion of methane gas obtainedfrom gas fields which contain little on no other gaseous hydrocarbonsother than methane.

BACKGROUND OF THE INVENTION

It is the business of many refineries and chemical plants to obtain,process and upgrade relatively low value hydrocarbons to more valuablefeeds, or chemical raw materials. For example, methane, the simplest ofthe saturated hydrocarbons, is often available in rather largequantities either as an undesirable by product in admixture with othermore valuable higher molecular weight hydrocarbons, or as a component ofan off gas from a process unit, or units. Though methane is useful insome chemical reactions, e.g., as a reactant in the commercialproduction of methanol and formaldehyde, it is not as useful a chemicalraw material as most of the higher molecular weight hydrocarbons. Forthis reason process streams which contain methane are usually burned asfuel.

Methane is also the principal component of natural gas, which iscomposed of an admixture of normally gaseous hydrocarbons ranging C₄ andlighter and consists principally of methane admixed with ethane,propane, butane and other saturated, and some unsaturated hydrocarbons.Natural gas is produced in considerable quantities in oil and gasfields, often at remote locations and in difficult terrains, e.g.,offshore sites, arctic sites, swamps, deserts and the like. Under suchcircumstances the natural gas is often flared while the oil isrecovered, or the gas is shut in, if the field is too remote for the gasto be recovered on a commercial basis. The construction of pipelines tocarry the gas is often not economical, due particularly to the costs ofconnecting numerous well sites with a main line. Transport of naturalgas under such circumstances is also uneconomical because methane atatmospheric pressure boils at -258° F. and transportation economicsdictate that the gas be liquefiable at substantially atmosphericpressures to reduce its volume. Even though natural gas containscomponents higher boiling than methane, and such mixtures can beliquefied at somewhat higher temperatures than pure methane, thetemperatures required for condensation of the admixture is nonethelesstoo low for natural gas to be liquefied and shipped economically. Underthese circumstances the natural gas, or methane, is not even ofsufficient value for use as fuel, and it is wasted.

The thought of utilizing methane from these sources, particularlyavoiding the tremendous and absolute waste of a natural resource in thismanner, has challenged many minds, but has produced few solutions. It ishighly desirable to convert methane to hydrocarbons of higher molecularweight (hereinafter, C₂ +) than methane, particularly admixtures of C₂ +hydrocarbon products which can be economically liquefied at remotesites; especially admixtures of C₂ + hydrocarbons rich in ethylene orbenzene, or both. Ethylene and benzene are known to be particularlyvaluable chemical raw materials for use in the petroleum, petrochemical,pharmaceutical, plastics and heavy chemicals industries. Ethylene isthus useful for the production of ethyl and ethylene compounds includingethyl alcohol, ethyl ethers, ethylbenzene, styrene, polyethylbenzenesethylene oxide, ethylene dichloride, ethylene dibromide, acetic acid,oligomers and polymers and the like. Benzene is useful in the productionof ethylbenzene, styrene, and numerous other alkyl aromatics which aresuitable as chemical and pharmaceutical intermediates, or suitable inthemselves as end products, e.g., as solvents or high octane gasolinecomponents.

It has been long known that methane, and natural gas can bepyrolytically converted to C₂ + hydrocarbons. For example, methane ornatural gas passed through a porcelain tube at moderate red heat willproduce ethylene and its more condensed homologs such as propylene, aswell as small amounts of acetylene and ethane. Methane and natural gashave also been pyrolytically converted to benzene, the benzene usuallyappearing in measurable quantities at temperatures above about 1650° F.(899° C.), and perhaps in quantities as high as 6-10 wt. % at 2200° F.to 2375° F., (1204° to 1302° C.) or higher. Acetylene and benzene inadmixture with other hydrocarbons, have been produced from methane andnatural gas in arc processes, cracking processes, or partial combustionprocesses at temperatures ranging above about 2775° F. (1524° C.). Heatfor such reactions has been supplied from various sources includingelectrically heated tubes, electric resistance elements, and spark orarc electric discharges. These processes characteristically requireconsiderable heat energy which, most often, is obtained from combustionof the by-product gases. The extreme temperatures coupled with the lowyields of higher molecular weight hydrocarbons such as benzene an otheraromatics have made the operation of such pyrolytic processesuneconomical.

High temperature, noncatalytic, thermal pyrolysis processes involvingthe conversion of methane in the presence of ethane and otherhydrocarbons are well known in the art. Representative articles include:Roczniki Chemi, An. Soc. Chim. Polonorum, 51, 1183 (1977), "TheInfluence of Ethane on Thermal Decomposition of Methane Studied By TheRadio Chromatographic Pulse Technique"; J. Soc. Chem. Ind. (Trans. andComm.) 1939,58, 323-327; and J. Chin. Chem. Soc. (Taipei) 1983, 30(3),179-83.

Addition of hydrogen to pyrolysis reaction mixtures is well known, seefor example, pp. 84-85 in "Pyrolysis Theory and Industrial Practice", L.F. Albright, B. L. Crynes and W. H. Corcoran (Ed.), Academic Press(1983).

Partial oxidation processes of converting methane to C₂ + hydrocarbonsare well known. In these processes, hydrogen must be removed either aswater, molecular hydrogen or other hydrogen-containing species.Likewise, any other polymerization mechanism wherein methane isconverted to C₂ + hydrocarbon products requires a tremendous amount ofenergy, most often supplied as heat, to provide the driving force forthe reactions. In the past the molecular hydrogen liberated by thereaction has often been separated and burned to provide the necessaryprocess heat. This route has proven an abomination to the production ofC₂ + hydrocarbons, but alternate reaction pathways have appeared littlebetter, if any, for these have resulted in the production of largequantities of the higher, less useful hydrogen deficient polymericmaterials such as coke, and highly oxidized products such as carbondioxide and water.

Typical of low temperature prior art oxidation processes are thosedisclosed in U.S. Pat. Nos. 4,239,658, 4,205,194 and 4,172,180 which usea regenerable catalyst-reagent. U.S. Pat. No. 4,239,658, for example,teaches a process for the conversion of methane to higher molecularweight hydrocarbons. In the process, a three component catalyst-reagentis utilized which comprises a mixture of various metals and metaloxides, particularly a Group VIII noble metal, nickel or a Group VI-Bnoble metal, a Group VI-B metal oxide and a Group II-A metal. The patentteaches process temperatures from about 1150° to 1600° F. (621° to 871°C.), preferably 1250° F. to about 1350° F. (677° to 732° C.).

It has also been reported in Science 153, 1393, (1966), "HighTemperature Synthesis of Aromatic Hydrocarbons From Methane", thataromatic hydrocarbons can be prepared from methane by contact withsilica at 1000° C. (1832° F.). The yield of hydrocarbons was in therange of 4.8 to 7.2 percent based on the methane used in a single passat a space velocity of 1224 hr⁻¹.

In the J. Chinese Chem. Soc., Volume 29, pages 263-273 (1981), it isreported that methane can be converted to C₂ + hydrocarbons attemperatures of 800° to 1130° C. and space velocities of 3100 hr⁻¹ orless using a metal oxide catalyst. However, the total conversion ofmethane, at best, is 7.5 mole percent using a thorium oxide catalyst.

Franz Fischer, reports in an article entitled: "The Synthesis of BenzolHydrocarbons From Methane At Ordinary Pressure and Without Catalyst"(Brennstoff-Chemie, Vol. 9, pp. 309-316, 1928) that methane is convertedto benzol hydrocarbons by passing methane through a hot tube. Incarrying out this work Fischer tested many substances for catalyticactivity at temperatures ranging from 650° to 1150° C. and at high flowrates and concluded that the substances tested were not catalytic andnot necessary. Among the substances tested were elemental iron, copper,tungsten, molybdenum, tin and carbon; and the compounds potassiumhydroxide and silica gel.

SUMMARY OF THE INVENTION

In a continuous catalytic process for the production of higher molecularweight hydrocarbons from methane in which a methane-containing gas iscontacted in a reaction zone with a higher molecular weight hydrocarbonsynthesis catalyst under C₂ + hydrocarbon synthesis conditions, theimprovement comprising adding a C₂ to C₄ hydrocarbon and hydrogen tosaid gas thereby forming a reaction gas wherein said C₂ to C₄hydrocarbon comprises 0.1 to 10 volume percent of said reaction gas andsaid hydrogen comprises 1 to 25 volume percent of said reaction gas,said synthesis conditions including a temperature greater than 1000° C.and a gas hourly space velocity of greater than 3200 hr⁻¹.

DETAILED DESCRIPTION OF THE INVENTION

In our copending application entitled: "Enhancing the Production ofAromatics In High Temperature, High Space Velocity Catalytic Conversionof Methane To Higher Molecular Weight Hydrocarbons", filed Oct. 31,1985, the entire disclosure of which is incorporated herein byreference, it is disclosed that the addition of hydrogen to the feed gassignificantly increases the production of light aromatic hydrocarbons.It has now been found that although the amount of light aromatics isincreased by hydrogen addition, the addition of hydrogen has the adverseaffect of reducing the reaction rate.

In our copending application entitled: "Enhancing the Reaction Rate InHigh Temperature, High Space Velocity Catalytic Conversion Of Methane ToHigher Molecular Weight Hydrocarbons", filed Oct. 23, 1985, the entiredisclosure of which is incorporated herein by reference, it is disclosedthat by addition of a C₂ to C₄ hydrocarbon to the feed gas dramaticallyincreases the reaction rate.

It has been found that by the addition of a C₂ to C₄ hydrocarbon andhydrogen to the feed gas in the catalytic conversion of methane tohigher molecular weight hydrocarbons that the amount of light aromaticsis increased without significantly decreasing the reaction rate.

As used in the present invention the phrase "lower molecular weighthydrocarbons" means hydrocarbons containing at least one or more carbonatoms, i.e., methane, ethane, propane, etc. Also as used in the presentinvention, the phrase "higher molecular weight hydrocarbons" meanshydrocarbons containing two or more carboa atoms and at least one carbonatom more than the lower molecular weight hydrocarbon in the feedstock.

As used herein the phrase "C₂ + hydrocarbon synthesis conditions" refersto the selection of feedstock, reaction temperature, space velocity andcatalyst described hereafter such that higher molecular weighthydrocarbons are produced in the process with yields as describedhereafter. Other process parameters necessary to maintain C₂ +hydrocarbon synthesis conditions, such as the selection of particulartypes of reaction vessels, etc., is readily determined by any personskilled in the art.

As used in the present invention the word "metal" refers to all thoseelements of the periodic table which are not non-metals. "Non-metals"for the purpose of the present invention refers to those elements havingatomic numbers 1, 2, 5 through 10, 14 through 18, 33 through 36, 52through 54, 85 and 86.

The word "catalyst" is used in the present invention to mean a substancewhich strongly affects the rate of a chemical reaction but which itselfundergoes no chemical change although it may be altered physically bychemically absorbed molecules of the reactants and reaction products.

As used in the present invention the phrase "continuous catalyticprocess" means a process in which feedstock and products aresimultaneously fed to and removed from a reaction zone containing acatalyst.

As used in the present invention the phrase "reaction gas" refers to thegas being fed to the catalyst-containing reaction zone.

As used in the present invention the words "light aromatics" refers tosingle ring aromatic hydrocarbons, for example, benzene, toluene,xylenes, and so forth.

The Reaction Gas and Products

The reaction gas of the present invention will comprise methane andsufficient added C₂ to C₄ hydrocarbon to significantly increase thereaction rate and added hydrogen to increase the production of lightaromatics.

Enough C₂ to C₄ hydrocarbon is added to increase the reaction rate by afactor of 1.4 to 4.0 as compared to a reaction gas consisting of 100%methane. Generally, the C₂ to C₄ hydrocarbon is added so that thereaction gas comprises 0.1 to 10 volume percent added C₂ to C₄hydrocarbon. Preferably, the added C₂ to C₄ hydrocarbon content in thereaction gas comprises 1 to 5 volume percent and more preferably 2 to 4volume percent. The preferred hydrocarbon for addition to the feed gasis ethane. Other useful C₂ to C₄ hydrocarbons include ethylene,acetylene, propane, propylene, butane, mixtures thereof, etc.

Enough hydrogen is added to increase the the yield of light aromatichydrocarbons by 10 to 40 weight percent as compared to a reaction gasconsisting of 100% methane. Generally, the hydrogen is added so that thereaction gas comprises 1 to 25 volume percent added hydrogen.Preferably, the added hydrogen content in the reaction gas comprises 2to 20 volume percent and more preferably 5 to 15 volume percent.

The reaction gas can also contain other nonhydrocarbon gases such asnitrogen and carbon dioxide.

Preferably the reaction gas is made from a methane-containing gas whichis obtained from a gas field which contains little or no hydrocarbonsother than methane. Preferably the reaction gas is made from a methanecontaining gas comprising more than 95 volume percent methane and lessthan 1 volume percent other hydrocarbons. More preferably, the reactiongas is made from a methane containing gas containing less than 0.2volume percent hydrocarbons other than methane.

The product higher molecular weight hydrocarbons will comprise C₂ +hydrocarbons, particularly mixtures of C₂ + hydrocarbons which can beeconomically liquefied. Preferably, the higher molecular weighthydrocarbon product streams will be rich in ethylene or aromatics suchas benzene, or both. The product stream will also contain copiousamounts of hydrogen. The hydrogen and C₂ to C₄ hydrocarbon added to thefeed gas can of course be obtained from the product gas.

The process of the present invention affords high conversions of themethane with high selectivity to higher molecular weight hydrocarbons.More particularly, as measured by the disappearance of methane, theprocess of the present invention affords conversions of 19 mole percentor more of the methane, and preferably, the conversions are greater than25 mole percent and more preferably greater than 40 mole percent. Thecarbon-containing reaction products comprise 80 mole percent or more ofhigher molecular weight hydrocarbons, preferably, greater than 90 molepercent. Based on the feed, at least 15 mole percent, and preferably atleast 20 mole percent, and more preferably at least 40 mole percent ofthe methane is converted to higher molecular weight hydrocarbons whichis referred to herein as selectivity.

The product higher molecular weight hydrocarbons will comprise C₂ +hydrocarbons, particularly mixtures of C₂ + hydrocarbons which can beeconomically liquefied. Preferably, the higher molecular weighthydrocarbon product streams will be rich in ethylene or aromatics suchas benzene, or both.

Process Conditions

It is essential to the process of the present invention that a hightemperature greater than 1000° C. is maintained in the reaction zonealong with a high gas hourly space velocity of greater than 3200 hr⁻¹.Preferably, the temperature will be greater than 1020° C. with a spacevelocity greater than 6000 hr⁻¹. Still more preferably the temperatureis less than 1150° C. with a space velocity greater than 9000 hr⁻¹.

Generally, the temperature will be in the range of 1001° to 1300° C.while the gas hourly space velocity is in the range 3200 to 360,000hr⁻¹. Preferably, the temperature is in the range 1020° to 1150° C. witha gas hourly space velocity of 6,000 to 36,000 hr⁻¹. More preferably thetemperature is in the range 1050° to 1125° C. with a gas hourly spacevelocity in the range of 9,000 to 18,000 hr⁻¹. Generally, hightemperatures are used with high space velocities and low temperaturesare used with low space velocities.

The process can be operated at sub-atmospheric, atmospheric, or supraatmospheric pressure to react and form the higher molecular weight C₂ +hydrocarbons. It is preferred to operate at atmospheric pressure orwithin about 15 psi of atmospheric pressure.

The Catalysts

The methane is introduced into a reaction zone containing a suitablehydrocarbon synthesis catalyst. The reaction-zone catalyst system can beeither of the fixed bed type or fluid bed type and the methane can beintroduced into the top or bottom of the reaction zone with the productstream removed from either the top or bottom. Preferably, a fixed bedcatalyst system is used and the feed stream is introduced into the topof the reaction zone and product is withdrawn from the bottom.

A wide range of catalysts can be used in the present invention. Manycommercially available catalysts which have been used in differentprocesses are suitable for use in the process of the present invention.The word "catalyst" is used in the present invention to mean a substancewhich strongly affects the rate of a chemical reaction but which itselfundergoes no chemical change although it may be altered physically bychemically absorbed molecules of the reactants and reaction products. Itis also understood that the catalyst of the present invention may beformed in situ. For example, in the present invention when an oxide,nitride, or carbide metal catalyst is initially charged to the reactor,the oxide and nitride may be converted in situ to the carbide which thenfunctions as the catalytic species.

Catalysts useful in the present invention may be used with and withoutcatalyst supports. However, it is generally preferred to use a catalystsupport such as the well known aluminas.

The catalysts useful in the present invention may have a wide range ofsurface areas as measured by the BET method using krypton [Jour. Am.Chem. Soc., vol. 60, pp. 309 (1938)]. Low surface areas are preferred.Generally, the catalyst will have a surface area in the range 0.1 to 10m² /gram, preferably in the range 0.2 to 2.0 m² /gram.

The hydrocarbon synthesis catalysts useful in the present invention willprovide conversion of at least 19% of the methane and will maintain thisconversion for at least 3 hours under the temperature and space velocityconditions previously discussed. Preferred catalysts of the presentinvention will provide conversions of 30% or more of the methane feedand remain active for 3 hours or more.

Particularly preferred catalysts are those described in our copendingapplication entitled "Conversion of Low Molecular Weight Hydrocarbons toHigher Molecular Weight Hydrocarbons Using a Metal-containing Catalyst",Ser. No. 547,699, filed October 31, 1983, the entire disclosure of whichis incorporated herein by reference. A useful silicon-containingcatalyst is disclosed in our copending application entitled:"Conversions of Low Molecular Weight Hydrocarbons to Higher MolecularWeight Hydrocarbons Using a Silicon Compound-Containing Catalyst", Ser.No. 547,697, filed Oct. 31, 1983, the disclosure of which isincorporated herein by reference. A useful boron compound containingcatalyst is described in U.S. Pat. No. 4,507,517, the disclosure ofwhich is incorporated herein by reference.

The hydrocarbon synthesis catalysts useful in the present invention maybe a metal compound-containing catalyst or non-metal compound-containingcatalyst or mixtures thereof.

Metal-Compound Containing Catalysts

A wide range of metal compound-containing catalysts and catalystsupports may be used in the present invention.

Representative metal compound-containing catalysts are refractorymaterials and include the compounds of the Group I-A, II-A, III-A, IV-Bor actinide series metals. Representative compounds include the carbide,nitride, boride or oxide of a Group I-A, II-A, III-A, IV-B or actinideseries metal, used alone or in combination.

The catalyst must be thermally stable under the operating condition inthe reaction zones and are preferably particulate in form. The carbidesof the Groups I-A, II-A, III-A, IV-B and actinide series metals areparticularly preferred because it is believed that the carbide metalcompound-containing catalyst are the most stable under the severereaction conditions of the present invention. Preferably, the catalystcan also be regenerated by the periodic burning-off of any undesirabledeposits such as coke. The regeneration of catalyst by the burning offcoke is well known in the catalyst and petroleum processing art.

Representative Group I-A metal compound-containing catalyst include thecarbide, nitride, boride, oxide of lithium, sodium, potassium, rubidium,and cesium. Most preferred among the Group I-A metals is lithium.

Representative Group II-A metal compound-containing catalysts includethe carbide, nitride, boride, or oxide of beryllium, magnesium, calcium,strontium, barium, and radium. Most preferred among the Group II-Ametals is calcium.

Representative Group III-A metal compound-containing catalysts includethe carbide, nitride, boride, or oxide of aluminum, scandium, yttrium,lanthanum, and actinium. Most preferred among the Group III-A metals isaluminum.

Representative Group IV-B metal compound-containing catalysts includethe carbide, nitride, boride, or oxide of titanium, zirconium, hafnium,and zirconium. Most preferred among the Group IV-B metals is zirconium.Representative actinide series metal compound-containing catalystsinclude the carbide, nitride, boride, or oxide of thorium and uranium.Most preferred among the actinide series metals is thorium.

A particularly preferred catalyst for use in the present invention isthorium oxide on alumina.

Non-Metal Compound Containing Catalysts

Representative non-metal compound containing catalysts are catalystscontaining compounds of boron and silicon.

Representative boron compound containing catalysts are refractorymaterials and include boron carbide, or boron nitride. Particularlypreferred is boron nitride.

Representative silicon compound-containing catalysts are refractorymaterials and include silicon carbide, nitride, silicon boride orsilicon oxide. Particularly preferred is silicon carbide.

The advantages of the present invention will be readily apparent from aconsideration of the following examples.

The examples illustrating the invention were carried out as follows:

EXAMPLES

Addition of hydrogen to a methane feed gas to the reaction zone of thesubject catalytic process decreases the conversion of methane (at aconstant temperature and gas hourly space velocity). Addition of C₂ toC₄ hydrocarbons to a methane feed gas to the reaction zone of thesubject catalytic process increases methane conversion. Addition of bothhydrogen and C₂ to C₄ hydrocarbons to methane feed gas to the reactionzone of the subject catalytic process increases selectivity andconversion, as shown in the examples below.

Examples 1 and 2

The apparatus of these examples comprises a vertical reactor tube madeof high purity alumina of 3/8" O.D. and 1/4" I.D. This tube is 24" long,the central 12" of which is surrounded by a high temperature electricfurnace (Marshall Model 1134). The heated section of the tube is packedwith the test catalyst. A small piece of close fitting aluminahoneycomb, or monolith, at the bottom of the bed supports the catalyst.An "O"-ring sealed closure at the top of the reactor tube connects it toa gas flow system, which permits either argon or methane to be passedinto the reactor at a measured rate. Gas flows into the reactor aremeasured with precalibrated flowmeters. Gas exiting from the reactor isfirst passed through a trap packed with dry stainless steel "saddles"(distillation column packing), then through a tube fitted with a rubberseptum. Gas samples are taken through the septum with a syringe. Off gasexits the system through a "U"-tube partially filled with oil. Bubblespassing through the oil provide a visual indicator of the gas flow.

In operation, the central section of the reactor tube is packed with thecatalyst to be tested. The catalyst particles range in size from 8 meshto 12 mesh. About 10 cm³ of catalyst is charged to the reactor. Thereactor is then placed in the cold furnace, and the necessary input andoutput connections are made. A slow flow of about 15 to 20 ml/min. ofargon is continuously passed through the reactor, which is then broughtto the desired temperature over a period of about 150 min. Temperaturesreported herein are measured in the furnace wall. Temperatures aremeasured by a thermocouple mounted in the furnace wall. Calibrationcurves, previously developed from a thermocouple in the catalyst bed andcompared to the furnace wall thermocouple, are used to determine thereaction temperatures reported herein.

Once the apparatus is at the desired temperature, argon flow is stoppedand methane flow is started at the predetermined flow rate. Spacevelocities are calculated on the basis of the temperature, pressure,methane flow rate into the reactor and on the catalyst bed dimensions.On each run, the reaction is allowed to level out for 15 to 20 minutesbefore the first analytic sample is withdrawn through the septum. Twosamples are taken each time, using one ml gas-tight syringes. Aliquotsof these samples (0.25 ml) are separately injected into a gaschromatograph packed with Poropak Q. Analysis is made for hydrogen,methane, and light hydrocarbons having less than atoms of carbon. Otheraliquots of the same samples are injected into another gas chromatographcolumn packed with Bentone 1200. This analysis is made for aromatics,including benzene, toluene, xylenes, etc.

The conditions and results of Examples 1 and 2 are shown in Tables 1 and2, respectively.

                  TABLE 1                                                         ______________________________________                                        CONSTANT CONVERSION OF 30%, GHSV = 9,000 HR.sup.-1                                     % H.sub.2                                                                              % C.sub.2 H.sub.4                                                                       % of Converted                                    Temperature                                                                            in Feed  in        Carbon Atoms Appearing                            °C.                                                                             Gas      Feed Gas  as Light Aromatics                                ______________________________________                                        1160     0        0         21                                                1125     0        3         26                                                1150     15       3         22                                                ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        CONSTANT TEMPERATURE OF 1100°  C.,                                     GHSV -12,000 HR.sup.-1                                                        % H.sub.2                                                                             % C.sub.2 H.sub.4   % of Converted                                    in Feed in        Conversion                                                                              Carbon Atoms Appearing                            Gas     Feed Gas  %         as Light Aromatics                                ______________________________________                                        0       0         9.1       9.6                                               0       5         22        32                                                15      5         20        39                                                ______________________________________                                    

Example 3

The apparatus for Example 3 was similar to that described above forExamples 1 and 2 except that the inside diameter of the reactor was 1/2inch and contained a 1/4 inch outside diameter thermal well. At thecompletion of the run, the feed gas was replaced by argon and air inorder to oxidize the coke. The amount of coke was determined from thetotal amount of carbon dioxide formed by oxidation.

With the coke weight, the known inlet and exit flows, and the gasanalysis results, the fraction of methane converted to coke wascalculated. Light hydrocarbons and aromatics were determined from thegas analysis and flow information. Heavy hydrocarbons (C₁₀₊) were thencalculated by difference. Auxilary experiments, in which the heavyhydrocarbons were analyzed by three different methods (gaschromatography, gas chromatography-mass spectroscopy and by liquidchromatography) showed what fraction of the heavy hydrocarbons consistedof 2 ring, 3 ring, and 4 ring fused aromatics, their isomers andalkylated derivatives. This correction factor was then applied todetermine the yield of the 1 through 4 ring aromatics.

The conditions and results of Example 3 are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        CONSTANT TEMPERATURE OF 1040° C.,                                      GHSV 12,000 HR.sup.-1                                                         % H.sub.2                                                                              % C.sub.2 H.sub.6                                                    in Feed  in            Conversion                                                                              %                                            Gas      Feed Gas      %         Yield                                        ______________________________________                                        0        0             14        48                                           0        3             16        64                                           7.5      3             14        69                                           ______________________________________                                    

The above data demonstrates that adding hydrogen to the feed gasdecreases conversion, directly evident in Tables 2 and 3 and evident bythe increase in temperature required to maintain 30% conversion inTable 1. Addition of both hydrogen and a C₂ hydrocarbon to the feed gasincreases the selectivity of the process, affording a larger fraction ofconverted carbon appearing as light aromatics in Tables 1 and 2 and alarger yield in Table 3.

In Table 3, the % yield was calculated as follows: ##EQU1##

The weight of aromatics products from methane was found as follows. Thenumber of moles of each aromatic product including one ring through fourrings (i.e., benzene and benzene derivatives through pyrene and itsisomers and derivatives), was determined. The fraction of carbon atomsin each of these products that originated from methane was calculated onthe assumption that the fraction of carbon atoms in each product due tomethane was the same as the fraction of carbon atoms due to convertedmethane. The proportion of moles of each product due to methane wascalculated. Multiplying the number of moles of each product by itscorresponding molecular weight then afforded the weight of each product.Summing these weights was then the weight of useful products frommethane.

The catalyst for Table 1 was prepared as follows. A low area support wasprepared by crushing Carborundum Company fused white refractory aluminabubbles, sieving the crushed material and retaining the 8-20 meshfraction. To 20 g of this support was added dropwise a solution of 1.23g Th(NO₃)₄. 4H₂ O in 2 ml distilled water and then a solution of 2.21 gLa(NO₃)₃.6H₂ O in 2 ml distilled water. During addition of the solutionthe support was stirred with a spatula, then thoroughly mixed for 5minutes once addition was complete. The mixture was dried in a 160° C.oven for 3 hours, then calcined in air at 900° C. to decompose thenitrates to the oxides.

The reaction tube was coated with copper by mechanically rotating thehorizontal reaction tube with a stream of nitrogen passing through it,and adding dropwise a saturated solution of cupric nitrate in methanol.The resulting tube, internally coated with cupric nitrate, was fired at1000° C. to decompose the nitrate to the oxide. The cupric oxide coatingis quickly reduced by methane under synthesis conditions to metalliccopper.

The catalyst used for Tables 2 and 3 was prepared as follows. A solutionof 67.13 g Th(NO₃)₃.4H₂ O and 105.30 g La(NO₃)₃.6H₂ O in 245 mldistilled water was prepared. To this solution was added dropwise, andwith continuous stirring, a 10% excess of a 10% by weight aqueoussolution of oxalic acid. A fine white precipitate of the oxalate ofTh⁺⁺⁺⁺ and La⁺⁺⁺ is formed. Stirring was continued several hours afterthe oxalic acid solution addition was complete. The precipitate wasallowed to settle, and the supernatant liquid decanted. After washingtwice (the wash waters were decanted) with about 2 liters of distilledwater, the precipitate was collected on a Buchner funnel and allowed todry at room temperature on the funnel. The dried material was thencalcined in air at 650° C. for 2 hours, which converts the oxalates tothe oxides. Pellets of the mixed oxide were prepared by adding 7.5% (byweight) ammonium stearate to the fine white calcined powder, andpelletizing this mixture in a pellet press. The resulting pellets werethen calcined in air in a muffle furnace, the temperature of which wasraised from room temperature to 1000° C. over a period of 4 hours. Whilestill hot (about 400° C.) they were transferred to a vacuum ovenmaintained at 120° C. for storage (to avoid slaking the La₂ O₃).Immediately before use, the pellets were crushed, sieved and the 12-20mesh fraction loaded in the reactor tube, through which an argon flowwas maintained to keep the catalyst dry. On top of the catalyst bed wereplaced 5 g of a prebed of 5% (by weight) copper on Carborundum Companywhite fused refractory alumina.

What is claimed is:
 1. In a continuous catalytic process for the theproduction of higher molecular weight hydrocarbons from methane in whicha methane-containing gas containing less than 1 volume percent otherhydrocarbons is contacted in a reaction zone with a higher molecularweight hydrocarbon synthesis catalyst under C₂ + hydrocarbon synthesisconditions, the improvement comprising increasing the reaction rate ofsaid methane-containing gas by a factor of 1.4 to 4.0 by adding a C₂ toC₄ hydrocarbon to said gas and increasing the yield of light aromatichydrocarbons by 10 to 40 weight percent by adding hydrogen to said gasthereby forming a raection gas wherein said C₂ to C₄ hydrocarboncomprises 0.1 to 10 volume percent of said reaction gas and saidhydrogen comprises 1 to 25 volume percent of said reaction gas, saidsynthesis conditions including a temperature greater than 1000° C. and agas hourly space velocity of greater than 3200 hr⁻¹.
 2. The process ofclaim 1 wherein said reaction zone contains a stationary or fluidizedbed of a catalyst containing a carbide, nitride, boride or oxide of aGroup I-A, II-A, III-A, IV-B or actinide series metal.
 3. The process ofclaim 2 wherein said temperature is in the range of 1100° to 1200° C.,said space velocity is in the range of 6000 to 36,000 hr⁻¹ and at least20 mole percent of said methane is converted to higher molecular weighthydrocarbons.
 4. The process of claim 3 wherein said added C₂ to C₄hydrocarbon comprises 1 to 5 volume percent of the reaction gas and saidhydrogen comprises 2 to 20 volume percent of the reaction gas.
 5. Theprocess of claim 4 wherein said catalyst contains a Group I-A metalselected from lithium, potassium or cesium.
 6. The process of claim 4wherein said catalyst contains a Group II-A metal selected fromberyllium, magnesium, calcium, strontium, barium or radium.
 7. Theprocess of claim 4 wherein said catalyst contains a Group III-A metalselected from aluminum, scandium, yttrium, lanthanum and actinium. 8.The process of claim 4 wherein said catalyst contains a Group IV-B metalselected from titanium, zirconium, and hafnium.
 9. The process of claim1 wherein said catalyst contains thorium or uranium.
 10. The process ofclaim 1 wherein said catalyst contains a boron compound.
 11. The processof claim 1 wherein said catalyst contains a silicon compound.
 12. Theprocess of claim 4 wherein said higher molecular weight hydrocarbonstream is rich in ethylene or aromatics or both.
 13. In a continuouscatalytic process for the production of higher molecular weighthydrocarbons from methane in which a methane-containing gas containingless than 0.2 volume percent other hydrocarbons is contacted in areaction zone with a higher molecular weight hydrocarbon synthesiscatalyst under C₂ + hydrocarbon synthesis conditions, the improvementcomprising increasing the reaction rate of said methane-containing gasby a factor of 1.4 to 4.0 by adding a C₂ to C₄ hydrocarbon to said gasand increasing the yield of light aromatic hydrocarbons by 10 to 40weight percent by adding hydrogen to said gas thereby forming a reactiongas wherein said C₂ to C₄ hydrocarbon comprises 1 to 5 volume percent ofsaid reaction gas and said hydrogen comprises 2 to 20 volume percent ofsaid reaction gas, said synthesis conditions including a temperature inthe range of 1050° to 1125° C., a space velocity is in the range of 9000to 18,000 hr⁻¹ and wherein at least 40 mole percent of said methane isconverted to higher molecular weight hydrocarbons.
 14. The process ofclaim 13 wherein said catalyst contains a Group I-A metal selected fromlithium, potassium or cesium.
 15. The process of claim 13 wherein saidcatalyst contains a Group II-A metal selected from beryllium, magnesium,calcium, strontium, barium or radium.
 16. The process of claim 13wherein said catalyst contains a Group III-A metal selected fromaluminum, scandium, yttrium, lanthanum and actinium.
 17. The process ofclaim 13 wherein said catalyst contains a Group IV-B metal selected fromtitanium, zirconium, and hafnium.
 18. The process of claim 13 whereinsaid catalyst contains thorium or uranium.
 19. The process of claim 13wherein said catalyst contains boron compound.
 20. The process of claim13 wherein said catalyst contains a silicon compound.
 21. The process ofclaim 13 wherein said higher molecular weight hydrocarbon stream is richin ethylene or aromatics or both.
 22. In a continuous catalytic processfor the production of higher molecular weight hydrocarbons from methanein which a gas consisting essentially of methane and containing lessthan 0.2 volume percent other hydrocarbons is contacted in a reactionzone with a higher molecular weight hydrocarbon synthesis catalyst underC₂ + hydrocarbon synthesis conditions, the improvement comprisingincreasing the reaction rate of said gas by a factor of 1.4 to 4.0 byadding a C₂ to C₄ hydrocarbons to said gas and increasing the yield oflight aromatic hydrocarbons by 10 to 40 weight percent by addinghydrogen to said gas thereby forming a reaction gas wherein said C₂ toC₄ hydrocarbon comprises 2 to 4 volume percent of said reaction gas andsaid hydrogen comprises 5 to 15 volume percent of the reaction gas, saidsynthesis conditions including a temperature in the range of 1050° to1125° C., a space velocity is in the range of 9000 to 18,000 hr⁻¹, saidcatalyst contains a carbide, nitride, boride or oxide of a Group I-A,II-A, III-A, IV-B or actinide series metal and wherein at least 40 molepercent of said methane is converted to higher molecular weighthydrocarbons.